Non-woven webs for many end uses, including filtration media, have been manufactured for many years. Such structures can be made from bicomponent or core shell materials. Filtration media made from bicomponent materials are disclosed in, for example, Wincklhofer et al., U.S. Pat. No. 3,616,160; Sanders, U.S. Pat. No. 3,639,195; Perrotta, U.S. Pat. No. 4,210,540; Gessner, U.S. Pat. No. 5,108,827; Nielsen et al., U.S. Pat. No. 5,167,764; Nielsen et al., U.S. Pat. No. 5,167,765; Powers et al., U.S. Pat. No. 5,580,459; Berger, U.S. Pat. No. 5,620,641; Hollingsworth et al., U.S. Pat. No. 6,146,436; Berger, U.S. Pat. No. 6,174,603; Dong, U.S. Pat. No. 6,251,224; Amsler, U.S. Pat. No. 6,267,252; Sorvari et al., U.S. Pat. No. 6,355,079; Hunter, U.S. Pat. No. 6,419,721; Cox et al., U.S. Pat. No. 6,419,839; Stokes et al., U.S. Pat. No. 6,528,439; Amsler, U.S. Pat. No. H2,086, U.S. Pat. No. 5,853,439; U.S. Pat. No. 6,171,355; U.S. Pat. No. 6,355,076; U.S. Pat. No. 6,143,049; U.S. Pat. No. 6,187,073; U.S. Pat. No. 6,290,739; and U.S. Pat. No. 6,540,801; U.S. Pat. No. 6,530,969; Chung et al., U.S. Pat. No. 6,743,273; Chung et al., U.S. Pat. No. 6,924,028; Chung et al., U.S. Pat. No. 6,955,775; Chung et al., U.S. Pat. No. 7,070,640; Chung et al., U.S. Pat. No. 7,090,715; and Chung et al., U.S. Patent Publication No. 2003/0 106294. This application incorporates U.S. Pat. No. 7,314,497, issued Jan. 1, 2008, and U.S. Publication No. 2009/0044702 published Feb. 19, 2009 by reference in their entirety. Such structures have been applied and made by both air laid and wet laid processing and have been used in fluid, both gaseous and air and aqueous and non-aqueous liquid filtration application, with some degrees of success.
Substantial prior art surrounding the use of bicomponent media in filter assemblies is directed to heating, ventilating, or air conditioning (HVAC) applications. For example, Arnold et al., U.S. Pat. No. 6,649,547, disclose a nonwoven laminate suitable for use as a filter for HVAC applications. The laminate has a microfiber layer integrated with a high loft multicomponent spunbond layer on one side and a low-loft multicomponent spunbond fiber on the other side. Preferably, the layers are through-air bonded and electret treated. Pike et al., U.S. Pat. No. 5,721,180 disclose a laminate filter media for HVAC applications, where first layer is electret high loft, spunbond crimped fiber web of low density and a second layer is electret meltblown microfiber layer having at least one polyolefin. Cusick et al., U.S. Pat. Nos. 5,800,586; 5,948,344; and 5,993,501, disclose a pleated composite filter media having randomly oriented fibers for use in HVAC type applications, e.g. automobile cabin air filtration. One or more thin stiffening layers help the construction retain its pleated formation, but the stiffening layer may also aid in filtration of dirt from air. Schultink et al., U.S. Pat. Nos. 7,094,270; 6,372,004; and 6,183,536, disclose a multiple layer filter for HVAC type applications or vacuum cleaner bags. Layers of filter media are bonded together in a laminate.
Air filtration applications such as HVAC applications involve a relatively low velocity of air through the filter media pack, for example less than 5 feet per minute (fpm). Other gaseous filtration applications include diesel engine crankcase ventilation (CCV) applications. CCV filters made from stacked, multiple layers of air laid and wet laid filtration media formed from bicomponent materials are described, for example, in U.S. Publication No. 2009/0044702 published Feb. 19, 2009, which is incorporated herein by reference in its entirety. Engine filtration applications for vehicles such as industrial diesel truck engines typically involve ventilation gas intake velocities of up to about 100 fpm. However, there are no filtration media formed from bicomponent materials that address high velocity air filtration applications, wherein intake air velocity exceeds 100 fpm or, in some applications, exceeds 500 fpm or even 600 fpm. Some air filtration applications, such as aviation inlet barrier filtration applications, involve air velocity of between about 500 fpm and 3000 fpm of air through the intake side of a filter element. Inlet barrier filters (IBF) are employed in high performance engines such as those used in civilian and military helicopters, or other turboprop type vehicle engines; other aviation engines such as jet engines; other high speed gas turbine engines; high power diesel or gasoline engines; and the like. IBF are employed to remove airborne particulates from the air intake path of the engine. Such particulates are of particular concern in helicopter engines, where large amounts of dust and debris are stirred up by the helicopter blades while the engine is engaged but the vehicle is grounded.
Conventional inlet barrier filters for high velocity applications are made from layers of oiled cotton gauze. The filters are typically reusable. When the filter becomes clogged and dirty, it is washed with plain water or water plus a detergent or another chemical additive supplied by the manufacturer, followed by drying and then reapplication of oil to the gauze layer before reuse. The cleaning cycle, from wash to reapplication of oil, can take as long as 24 hours including drying of the filter which must be done before oil can be reapplied. Labor time in washing and reapplication of oil is typically about 2-3 hours. The environmental, time, and cost impact of using oil-wetted media is burdensome.
To be useful in high velocity filter applications, filter media must be robust and yet allow for fast throughput of air, yet efficiently separate airborne particulates and debris from the air stream in order to protect the engine. Conventional wisdom dictates that higher velocity throughput requires thicker media in order to accomplish the required robustness in conjunction with satisfactory removal of particulates from gaseous streams moving at high velocity. However, thinner media allows higher velocity streams to pass through the filter without undue pressure drop. Thinner media are more easily washed and more quickly dried. Thus, there is a need for a robust, yet thin, high velocity air filter media that is effective in removing dust, dirt, and debris from the air intake path of engines where air intake rate is 100 fpm or above. There is a need for a high velocity air filter assembly that is easily and quickly washed with plain water. There is a need for a high velocity air filter that can be quickly removed, washed, and replaced on an engine without long periods of air drying and without use of oil.